{{For|other dioxin compounds|dioxin}} {{Chembox | Verifiedfields = changed | Watchedfields = changed | verifiedrevid = 477204382 | ImageFile = 1,2-dioxin.svg | ImageSize = 100 | ImageName = Skeletal formula of 1,2-dioxin | ImageFileL1 = 1,2-Dioxin-3D-balls 2.png | ImageFileR1 = 1,2-Dioxin-3D-spacefill.png | ImageName1 = Ball and stick model of 1,2-dioxin | PIN= 1,2-Dioxine | SystematicName = 1,2-Dioxacyclohexa-3,5-diene |Section1={{Chembox Identifiers | CASNo_Ref = {{cascite|changed|??}} | CASNo = 289-87-2 | UNII_Ref = {{fdacite|correct|FDA}} | UNII = R8H79L3J69 | PubChem = 15559065 | ChemSpiderID = 10606250 | ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}} | SMILES = O1OC=CC=C1 | StdInChI = 1S/C4H4O2/c1-2-4-6-5-3-1/h1-4H | StdInChI_Ref = {{stdinchicite|correct|chemspider}} | InChI = 1/C4H4O2/c1-2-4-6-5-3-1/h1-4H | StdInChIKey = VCZQYTJRWNRPHF-UHFFFAOYSA-N | StdInChIKey_Ref = {{stdinchicite|correct|chemspider}} | InChIKey = VCZQYTJRWNRPHF-UHFFFAOYAH }} |Section2={{Chembox Properties | C=4 | H=4 | O=2 }} |Section3={{Chembox Related | OtherCompounds = [[Dibenzodioxin]]<br /> [[1,4-Dioxin]] }} }}
'''1,2-Dioxin''' is a [[heterocyclic compound|heterocyclic]], [[Organic compound|organic]], [[Antiaromaticity|antiaromatic]]<ref>{{Cite journal |last1=Pelloni |first1=Stefano |last2=Faglioni |first2=Francesco |last3=Lazzeretti |first3=Paolo |date=2013-09-01 |title=Parity violation energies of C4H4X2 molecules for X = O, S, Se, Te and Po |url=https://doi.org/10.1080/00268976.2013.794396 |journal=Molecular Physics |volume=111 |issue=16–17 |pages=2387–2391 |doi=10.1080/00268976.2013.794396 |s2cid=100861633 |issn=0026-8976|url-access=subscription |hdl=11380/942493 |hdl-access=free }}</ref> [[chemical compound|compound]] with the [[chemical formula]] C{{sub|4}}H{{sub|4}}O{{sub|2}}. It is an [[isomer]]ic form of [[1,4-Dioxin|1,4-dioxin]] (or ''p''-dioxin).
:[[File:Dioxin isomers.svg|thumb|left|1,2-Dioxin (left) and 1,4-dioxin (right)]]{{clear-left}}
Due to its [[peroxide]]-like characteristics, 1,2-dioxin is very unstable and has not been isolated. Calculations suggest that it would [[isomerize]] rapidly into but-2-enedial.<ref>{{Cite book|last=Matsumoto|first=M.|chapter-url=https://books.google.com/books?id=Ah6GAwAAQBAJ&pg=PA13|title=Science of Synthesis: Houben-Weyl Methods of Molecular Transformations Vol. 16: Six-Membered Hetarenes with Two Identical Heteroatoms|publisher=Georg Thieme Verlag|year=2014|isbn=9783131718815|pages=13|chapter=Product Class 1: 1,2-Dioxins and Benzo- and Dibenzo- Fused Derivatives|access-date=2020-06-12}}</ref> Even [[Substitution reaction|substituted]] [[Derivative (chemistry)|derivatives]], such as 1,4-diphenyl-2,3-benzodioxin, are very [[labile]].<ref>{{Cite journal | doi = 10.1021/ja00368a021| title = Chemiluminescence of organic peroxides. Thermal generation of an o-xylylene peroxide| journal = Journal of the American Chemical Society| volume = 104| issue = 4| pages = 1041| year = 1982| last1 = Smith| first1 = Jimmie P.| last2 = Schrock| first2 = Alan K.| last3 = Schuster| first3 = Gary B.}}.</ref>
:[[File:1,4-diphenyl-2,3-benzodioxin.svg|thumb|left|Structure of the transient 1,4-diphenyl-2,3-benzodioxin]]{{clear-left}}
In 1990, 3,6-bis(''p''-tolyl)-1,2-dioxin ('''1''') was incorrectly reported as the first stable derivative.<ref>{{Cite journal | doi = 10.1021/jo00300a026| title = Electron transfer to excited doublet states. Photoirradiation of 10-methylphenothiazine cation radical perchlorate in solutions of phenylacetylene and p-tolylacetylene in acetonitrile| journal = The Journal of Organic Chemistry| volume = 55| issue = 13| pages = 4086| year = 1990| last1 = Shine| first1 = Henry J.| last2 = Zhao| first2 = Da Chuan}}.</ref> It was subsequently shown that the initial compound was not a derivative of 1,2-dioxin, but a thermodynamically more stable [[diketone|dione]].<ref>{{Cite journal | doi = 10.1021/jo034305i| pmid = 12737603| title = Revised Structure of a Purported 1,2-Dioxin: A Combined Experimental and Theoretical Study| journal = The Journal of Organic Chemistry| volume = 68| issue = 10| pages = 4108–11| year = 2003| last1 = Block| first1 = Eric| last2 = Shan| first2 = Zhixing| last3 = Glass| first3 = Richard S.| last4 = Fabian| first4 = Jürgen}}</ref>
:[[File:Revised structure 1,2-Dioxin.svg|thumb|left|Dioxin (1) and dione form (2)]]{{clear-left}}
== References == {{Reflist}}
== External links == {{Portal|Chemistry }} * {{Commons category-inline}}
{{DEFAULTSORT:Dioxin, 1, 2-}} [[Category:Dioxins]] [[Category:Hypothetical chemical compounds]] [[Category:Antiaromatic compounds]]